An employer’s benefit wages shall be the wages paid by him which became benefit wages. With respect to any base period applicable to a benefit year commencing prior to November 4, 1979, an employer’s benefit wages with respect to any one individual shall include only the amount specified in Section 1502 of this Act as amended and in effect on November 9, 1977. With respect to each base period applicable to benefit years commencing on and after November 4, 1979 an employer’s benefit wages with respect to any one individual shall not exceed the total amount of wages paid to the individual by that employer during the base period, or $6,000, whichever amount is smaller, except that an employer’s benefit wages resulting from the payment of extended benefits to an individual shall not exceed 1/2 such total amount of wages, or $3,000, whichever is smaller. The sum of an employer’s benefit wages resulting from the payment to the same individual of both regular benefits with respect to his benefit year and extended benefits with respect to his eligibility period which began in that benefit year shall not exceed 1 1/2 times the individual’s base period wages, or $9,000, whichever is less.